With the advent of mobile data processing and communications, the necessity of a highly readable, user-friendly operator interface has become apparent. One solution that meets this need for portable electronic devices is a flat panel liquid crystal display (LCD) in tandem with electroluminescent (EL) backlighting. Inherent in this selection is the problem of providing a high-voltage alternating current (AC) power source, derived from a relatively low voltage battery, to the electroluminescent backlight panel.
Typically the solution to this problem requires a large transformer to drive the EL panel due to a high drive voltage and low panel drive frequency requirements. The requirement that a large transformer be used in conventional driver circuit designs makes EL backlighting undesirable as a choice for LCD backlighting, due to the size, cost, and weight requirements of portable electronic devices. In addition, providing the user with the capability of adjusting the backlight brightness is essential for the wide array of usage environments that most portable electronic devices encounter. Electroluminescent backlight panels also exhibit undesirable aging characteristic that cause the luminance of the EL panel to decrease over time, due to the decrease in the panel capacitance.
The art has shown EL driver circuits using high-frequency switching converters to step up the drive voltage, thereby avoiding the use of a large transformer. Art has also shown aging compensation and user adjustment features. To be effective in a portable product, all of these requirements must be met. That one or more requisite attributes is lacking in all of the known and contemplated products has been shown. These feature can not merely be combined, but must be combined in a way that the resultant driver circuit can be easily implemented in a custom integrated circuit, in order to meet the cost and size requirements of a portable electronic device.
Clearly, a long felt need exists for an electroluminescent backlight panel driver circuit that is small and light-weight for application in portable electronic devices. Combined with the added enhancements of automatic aging compensation and user adjustment capability, a driver circuit that provides these advantages is absolutely required in the portable product arena.